Wood preservation treatments are needed to resist against weather erosion and worm eating. The most common wood preservation treatment is to immense wood in chromatic copper arsenate (which is briefly called as CCA). However, CCA is potentially hazardous, since children may intake arsenic chromium copper acids by touching outdoor playground facilities through a CCA wood preservation treatment. The prohibition of CCA as a wood preservation method induces the ACQ method. In that, wood is immersed into a solution of high copper ion content and a high pressure is applied to the solution to make the copper ions infiltrate into the wooden fibers. The copper ion concentration of the wood thereby produced is four times higher than that of the wood processed by CCA. The metallic parts embedded therein will be eroded. Structures made by ACQ wood may collapse after an extended period of time. To reduce the erosion in ACQ wood, the metallic parts in the wood should be processed through an anticorrosion treatment, which may be one of:
1. using metallic parts made of corrosion-resistant alloys;
2. coating the metallic parts with an impermeable covering;
3. treating the metallic parts by hot-dip Galvanic coating of zinc.
The screws used in wood structures are made of iron or other non-ironic alloys. The screws made of non-ironic alloys are expensive and too soft. Therefore, the application is limited.
An ironic material after heat treatment by carburizing becomes a carbon steel material which is mechanically tough and suitable for making parts associated with ACQ processed wood.
The carbon steel screws embedded within anticorrosive wood have their surfaces commonly plated with zinc by electrolysis and then inactivated by chromic acid. Finally, they will be protected by organic finishing. They look beautiful and will not be damaged when they are engaged with the wood. However, the anticorrosive ability of the parts is not satisfactory.
Further, the problem of pollution caused by Chromium-6 in the process of surface inactivation by a chromic acid cannot be ignored.